Chinese Journal of Electronics
Vol.23, No.2, Apr. 2014
Energy-Efficient Mapping for 3D NoC Using
Logistic Function Based Adaptive Genetic
Algorithms
∗
WANG Jiawen, LI Li, WANG Zhongfeng, ZHANG Rong and ZHANG Yuang
(Institute of VLSI Design, LAPEM, Nanjing University, Nanjing 210093, China)
Abstract — The problem of mapping application tasks
is one of key issues in 3D Network on chip (3D NoC) de-
sign. A novel Logistic function based adaptive genetic al-
gorithm (LFAGA) is proposed for energy-aware mapping
of homogeneous 3D NoC. We formulate the mapping prob-
lem and show the Standard genetic algorithm (SGA). The
LFAGA is presented in detail with the goal of obtaining
higher convergence speed while preventing the premature
convergence. Experimental results indicate that the pro-
posed LFAGA is more efficient than previously proposed
Chaos-genetic mapping algorithm (CGMAP). In the ex-
periments, a randomly generated task graph of size 27 is
mapped to a 3D NoC of size 3×3×3, the convergence speed
of LFAGA is 2.55 times faster than CGMAP in the best
condition. When the task size increases to 64 and the 3D
NoC size extends to 4×4×4, LFAGA is 2.31 times faster
compared to CGMAP. For the NoC sizes in the range from
3×3×2to4×4×4, solutions obtained by the LFAGA are
consistently better than the CGMAP. For example, in the
experiment of size 4×4×4, the improvement of final result
reaches 30.0% in term of energy consumption. For a real
application of size 3×4×2, 18.6% of energy saving can be
achieved and the convergence speed is 1.58 times faster
than that of the CGMAP.
Key words — Energy-aware mapping, 3D NoC, Logisitc
function, Adaptive genetic algorithm, Convergence speed.
I. Introduction
As the number of transistors on a chip continues to in-
crease, the traditional infrastructure cannot handle intensive
communications on chip effectively. Thus Network on chip
(NoC) was proposed as a promising alternative due to its per-
formance scalability and communication parallelism
[1,2]
.Typ-
ically, a NoC is formed by a global network which is composed
of a set of routers and computational or memory resources
which are connected to routers. Since the global network plays
a major role in the NoC design, lots of research groups have
paid special attentions on this aspect. However, according to
the NoC evolution, which forecasts that hundreds and even
thousands of cores will be integrated in one NoC in a few
years, the conventional two Dimensional (2D) interconnections
are considered as an inefficient architecture due to several in-
surmountable problems such as global wire length and packet
transfer delay. Meanwhile, relying on its potential to improve
chip performance, functionality, and device packing density
[3]
,
three Dimensional (3D) Integrated circuits (ICs) is emerging
as a novel approach. Considering the advantages of aforemen-
tioned technologies, 3D NoC is proposed as a combination of
both
[4]
to enhance architectural advantages of NoC.
Many challenges have to be faced during the design space
exploration of 3D NoC, and among all these issues, mapping is
one of key steps which may have great influence on the overall
system performance at the beginning of NoC design. Usually,
at early stages of a new design, the NoC communication back-
bone (e.g., the topology and the size) has to be decided first
and then a set of IP cores are chosen depending on various
kinds of tasks. After those tasks are assigned to different IP
cores and the Application characterization graph (APCG) is
formed (the accurate definition of APCG will be given in sec-
tion
¼
). Then the mapping problem can be defined as how
to topologically place the selected set of IP cores onto the re-
source nodes of the network such that the metrics of interest
are optimized
[5]
. In this work, we assume that steps before
mapping are already completed and we mainly focus on the
mapping problem.
There are two main challenges for NoC mapping as shown
in Fig.1: (1) an effective algorithm for mapping and (2) an
accurate model for solution evaluation. That is to say, firstly
we have to find a method to decide how to assign IPs to a par-
ticular topology, and secondly we have to build an analytical
modelsoastoevaluateifthemethodwechooseiseffectiveor
not. In this paper, we mainly focus on the first one. As we all
know that mapping is a quadratic assignment problem which is
Non-deterministic polynomial-time hard (NP-hard) and there
exists n! possible solutions for a 3D NoC of n nodes.
Since the exhaustive search algorithm is obviously infea-
sible, lots of approximation algorithms such as heuristic algo-
rithms have been proposed. Being one of the most important
∗
Manuscript Received Jan. 2012; Accepted May 2013. This work is supported in part by the National Nature Science Foundation
of China (No.61176024, No.61006018), Research Fund for the Doctoral Program of Higher Education of China (No.20120091110029), A
Project Funded by the Priority academic program development (PAPD) of Jiangsu Higher Education Institutions.